6 BULLETIN 992, U. S. DEPARTMENT OF AGPvICULTURE. 



punctured nuts and females were observed frequently to visit these 

 nuts, where copulation and oviposition took place. In approaching 

 these nuts the females usually came by easy stages, flying and crawl- 

 ing near the nut before alighting upon it. When the male would 

 observe a female approaching he would become much excited, moving 

 back and forth, whirling around, and raising and lowering the wings 

 in rapid succession, but remaining near the puncture made with the 

 nail point. On the arrival of the female upon the nut the male 

 would usually back away from the nail puncture a short distance 

 and there remain stationary, with wings elevated above the back, 

 watching the female intently. When the female would find the 

 puncture and start to insert the tip of her abdomen into the opening 

 for the purpose of depositing eggs, the male would spring upon her 

 and copulation would take place. There would then follow alter- 

 nating periods of oviposition and copulation, the male sometimes 

 continuing mounted while oviposition was in progress, and sometimes 

 dismounting but remaining near by. (PL III, d.) Frequently there 

 would be four or five periods of each before the female would fly 

 away. After this procedure the male was likely to continue on 

 guard at the same place, for the nail pricks were visited frequently 

 by ovipositing females. 



The flies were observed to be much more abundant on the lower 

 than on the higher branches of trees, and there was a great differ- 

 ence in the numbers of flies on individual trees of the same species. 

 On a group of heavy-laden Persian walnut trees of the variety 

 known as Hall, at West Willow, Pa., it was estimated that one fly 

 was present for every two nuts on the trees. The variation in the 

 numbers of flies on individual trees was followed by a corresponding 

 abundance or scarcity of maggots in the nuts of each. 



Flies were observed to feed upon the juice that flowed from ovi- 

 position scars and upon the naturally more or less gummy surface 

 of the nuts. In feeding they would eject from the mouth a particle 

 of clear liquid onto the surface and after working it over with the 

 purselike, external mouthparts would swallow it again. 



NATURE OF INJURY. 



In native black walnuts the eggs of the husk-maggot fly are 

 usually deposited so late in the season that the resultant maggots 

 do not prevent the nuts from maturing and dropping normally. 

 Thus, while apparently all the eggs are laid in nuts on the trees, 

 the development of the maggots and the blackening of the husks 

 which results from their feeding take place chiefly in fallen nuts. 

 In Persian walnuts, however, eggs appear to be laid earlier in the 

 development of the nuts. Bearing trees were observed in Maryland 

 and Pennsylvania, a short time before the crop had ripened, on which 



